1. Field of the Invention
This invention relates to condensation-crosslinkable dental materials, particularly condensation-crosslinkable two-component dental impression materials based on alkoxysilyl-functional and/or hydroxysilyl-functional polyethers, which are especially suitable for taking impressions. Such materials are used in dentistry, for example for taking tooth impressions, bite registration, denture rebasing, as temporary and permanent dental cement, temporary closure material, or dental prosthodontic material.
2. The Prior Art
Known condensation-crosslinking dental materials ordinarily contain hydroxy-functional polymers with a silicone backbone that harden in the presence of tin compounds as catalysts, alkoxysilanes and/or silicate esters as crosslinkers, and water. Of course, such materials are relatively hydrophobic because of the silicone backbone of the polymers, so that substantial proportions of surfactants have to be added to them to reduce surface tension and to establish the necessary wettability. Another drawback of these compositions is the use of toxicologically objectionable organic tin compounds as catalysts.
Alternatively to these, two-component dental materials are known that contain polymers having terminal alkoxysilyl groups with a hydrophilic polyether backbone, which have adequately hydrophilic properties for wetting the moist dental substance. These materials usually consist of a base component containing an alkoxysilyl-functional and/or hydroxysilyl-functional polyether with an average molecular weight of 800 to 20,000 g/mole, which may also have synthetically derived urea and/or urethane groups, fillers and optionally other additives, and a catalyst component that contains an organic and/or inorganic acid as catalyst in addition to fillers and optionally other auxiliaries. However, such materials, which are disclosed by European Patent Nos. EP 0 269 819 B1 and EP 1 226 808 A2, for example, have unsatisfactory properties for use because of the acid catalysis.
For this reason, base-catalyzed or salt-catalyzed hardening materials based on alkoxysilyl-functional polyethers have already been proposed. In International Publication No. WO 99/48942, organometallic compounds such as iron or tin compounds, for example tin (II) octanoate, or tertiary amines such as triethylamine are to be used as catalysts to crosslink polyurethanes that have polyether groups to be used as cements or sealants. However, the hardened vulcanizates/casts from these dental materials tend to lose their original shape by reversal of the crosslinking reaction (back-cleavage) after storage for some time at room temperature, and especially when stored at elevated temperature (e.g. 60° C.), and in extreme cases they tend to melt down with decomposition. Because of this, they are useless as a dental impression material since the finished impression may often be processed further to make a dental pattern only some time after taking the impression, or the impression has to be used again after a lengthy period of time (sometimes repeatedly) to make a dental pattern. Malformed or melted impressions then distort the dental pattern and lead to a useless dental prosthesis.